1. Field of the Invention
The present invention relates to a method of producing a flip chip and, more particularly, to a method of producing a flip chip by soldering.
2. Description of the Related Art
It is common practice to solder electronic parts by heating a flux applied thereto. This kind of soldering method is taught in, e.g., Japanese Patent Laid-Open Publication No. 3-050789 (JP-A-03-050789) or Japanese Patent Publication No. 64-001233 (JP-B2-64-001233). However, the problem with the soldering method using a flux is that an electronic part device must be rinsed after mounting because the flux is applied to the surface of the device to be soldered. This causes loads to act on portions where the device and a circuit board are connected, resulting in a defective product.
There is also available a soldering method not using a flux. This method positions pins studded on a presoldered LSI (Large Scale Integrated circuit) on solder bumps formed on a circuit board, and then heats them in an inactive atmosphere. In the inactive atmosphere, the oxide films of the solder bumps are broken by the weight of the package, forming soldered portions. While the presoldered films are formed by rinsing after the application of the flux, they do not matter at all because the flux can be removed before soldering. Such a fluxless soldering method is disclosed in, e.g., Japanese Patent Laid-Open Publication No. 3-106564 (JP-A-03-106564). However, because the pins are studded on the package, it is difficult to mount bare chip electrodes at a pitch as narrow as 120 .mu.m to 170 .mu.m by the above conventional method. Moreover, because the oxide films of the solder bumps are broken by the weight of the package, the method cannot fully break the oxide films when it comes to relatively small packages, bare chips or similar relatively light electronic parts.